Yes it is. I had never heard of it before, thanks for commenting.

Yes, and "steelmanning" is the stronger form of the idea.

The principle of charity more closely resembles a fairly complex skill with a lot of subskills. (That may be why it's so difficult and scarcely applied.) This is but one of them. (Others might be: assuming a common basis of reason and morality; do not ruin your relationship with the other person along the way; remember that there is such a thing as a state of mind (theirs) in which those beliefs are natural and obvious; etc.)